The present disclosure relates to a sensor that detects the amount or density of magnetic substance.
Some image forming apparatuses that use toner as developer adopt a system using one-component developer comprising toner containing magnetic substance (toner containing several percent of magnetic substance), while other image forming apparatuses adopt a system using two-component developer comprising non-magnetic toner and magnetic carrier. For the purpose of, with one-component developer, detecting the amount of toner and, with two-component developer, detecting the density of toner, a sensor that detects the amount or density of magnetic substance is used.
There is conventionally known, for example, a sensor that detects the amount or density of magnetic substance by use of a differential transformer.
It is occasionally necessary to detect a slight change in the amount or density of magnetic substance. For example, with one-component developer, as toner is fed to an electrostatic latent image, the amount of toner in a developing portion decreases, and new toner is supplied to the developing portion. It is necessary to keep the amount of toner in the developing portion constant so as to obtain a proper image. It is necessary to control the amount of toner by detecting a slight change in the amount of toner so as to obtain a high-quality image.
To detect a slight change in the amount or density of magnetic substance, the sensitivity of a sensor needs to be raised.